Whistler Reporting Rates

To: "'Kevin and Gwenyth Bray'" <>, <>
Subject: Whistler Reporting Rates
From: "Philip Veerman" <>
Date: Thu, 26 Apr 2012 23:27:42 +1000
Very good questions. Thanks for that. The GBS Report explains in huge and intimate detail everything you could possibly want to know about the sample size, the methods, the history, the biases and limitations. Although I often post extracts of individual species texts to this chat line to answer particular questions about a particular species, there is no way I am going to be posting whole slabs of the introductory section on a chat line. Read it! (Canberra Birds: A Report on the first 21 years of the Garden Bird Survey). If you can find and demonstrate any inadequacies in these aspects of The GBS Report (and after nearly 10 years no one yet has), it would be nice to know. And yes the results do have limitations and these are fully understood and explained therein. Show me a scientific report on natural populations that doesn't have limitations.
You refer to scientific data and analyses on Southern Bluefin Tuna (SBT) population coming from significant differences in the two countries' scientists' methodologies in estimating and I suggest no doubt differences in what they wished to prove. But the GBS is one system in one location. And yes the methods changed slightly during the course of the survey but this is explained in extreme detail in The GBS Report.
Maybe you are getting to the huge issue about whether the Canberra and region suburbia is representative of the wider SE Australian environment. Very good question. The GBS Report mentions but does not dwell on that issue, as it does not carry extra-regional data to make the comparison.
Yes as these are both common, widespread, easy to find and identify species, unlikely to be overlooked or misidentified, more than to a small amount that would be fairly constant over the years.  I am confident that the whistler (both species) sample areas used in the data/analysis that have are now being presented and discussed are "representative" enough, and the number of sightings made (whether positive or not) are large enough to enable reliable inferences to be drawn. Even if on some questions the inferences are that there is probably no change or not yet enough data to show a trend. More to the point, that is the data that we have. There is no other data against which to measure validate or compare these things. What is the alternative? People describe their individual vague impressions and we take that as a baseline and then say oh the survey data of 857483 individual count observations (over the first 21 years) on 53244 observer weeks and 1316 observer years (all these figures are much higher now) is less accurate than impressions!
Don't read Birds in Canberra Gardens for this. It is crap, crass, inadequate and deceptive in most respects of explaining these things.
Can people please learn the difference between the word "sites" (places) as in "actual bird sitings" which my spell check doesn't approve of and if it is a word would mean the actual place where some bird was and sights & sightings (observations).
-----Original Message-----From: Kevin and Gwenyth Bray [ Sent: Thursday, 26 April 2012 6:43 PM
To: Geoffrey Dabb;       Subject: Re: [canberrabirds] Whistler Reporting Rates

At risk of being (pretty rightly) accused of getting involved in something about which, in detail, I know very little (I'm a very amateur bird-watcher, though I do have qualifications in science and economics of some relevance to the question I'm asking!), I would be interested to know something about the statistical "reliability" of the data shown in the last few days on rufus and golden whistler population time series trends and population seasonalities.  My sense is that only if the data are statistically sound can reasonably reliable general conclusions be inferred from them.  (I'm not for one moment suggesting there is a "reliability problem" - it's just that I've not seen any comment on the question, either way).
I am wondering (a)  what sample sizes are these data based on - essentially how many actual bird sitings and how many "nil" sitings from how many observation sites/areas are represented by each data point on the graphs; and (b) what proportion of the "area/region of interest"  (eg, the ACT if it's trends in the ACT that are being reported)  - or perhaps more usefully what proportion of the species' typical habitat' in (say) the ACT, was included in the aggregate data?
I ask these questions, in part due to prior experience in ostensibly scientific data and analyses on Southern Bluefin Tuna (SBT) population, when I was involved as a policy adviser in trying to interpret the analyses from what had turned into a major dispute between Australian and Japanese fish population scientists over SBT populations and "responsible" fishing quotas. 
To simplify the detail of the analysis, the dispute turned on significant differences in the two countries' scientists' methodologies in estimating (and projecting) current and future SBT populations.  In part, an element in the different analyses and conclusions was the extent to which  population data from a set of "sample areas" which necessarily covered only a small proportion of the total range of SBT could, or could not, be regarded as "representative".
So, to put my questions that way, can you be confident that the whistler (both species) sample areas used in the data/analysis that have are now being presented and discussed are "representative" enough , and the number of sitings made (whether positive or not) large enough to enable reliable inferences to be drawn?
Thank you.
Kevin Bray

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